A quantitative procedure was developed for determining total flavonoids in horse chestnut buds (Aesculus hippocastanum L.) using differential spectrophotometry at 422 nm and recalculation as rhamnocitrin or 7-O-methylkaempferol (3,5,4′-trihydroxy-7-methoxyflavone), the dominant flavonoid in this raw material. The error of a single determination of total flavonoids in horse chestnut buds with 95% confidence probability was ± 2.23%. The contents of total flavonoids in horse chestnut buds varied from (1.24 ± 0.01) to (2.31 ± 0.03)%.